Heretofore, cargo lights used in various container trucks (such as refrigeration container trucks) are often fluorescent lights or incandescent lights, which suffer high power consumption, short service life due to being hard to properly operate in low temperatures, light irradiation containing harmful infrared or ultraviolet light, and bulkiness that hinders arrangement of cargos or commodities (for cargos might collide and impact the cargo light). Thus, light-emitting diodes (LED's) are sometimes used as replacement light sources.
A cargo light using LED as light source still shows several drawbacks:
(1) The interior of a cargo container is often cleaned by spraying water. However, the conventional cargo light is not provided with water resistant means that is strong enough to bear the spraying of intense water jets and this often leads to water penetration and thus malfunction of the cargo light. For a refrigeration container truck, to clean the interior of the refrigeration container, pressurized steam or hot water of approximately 80° C. is applied for washing and disinfection. The water resistance of the conventional cargo light is generally poor in this respect and is susceptible to deformation caused by heat expansion and cold contraction and this makes the problem of water penetration even worse and leads to malfunction caused by the penetrating water.
(2) When a container truck is traveling, it is subjected to continuous and repeated vibration. The conventional cargo light is not provided with vibration resistant means that is sufficient to handle such a situation of continuous vibration, eventually damaging the cargo light.
(3) Some conventional cargo lights use LED's as light source, but those LED's are made for indication purposes and having only very low luminance. Thus, even approximately 20-40 LED's are included in a single cargo light, the lighting range and the lighting performance provided by the cargo light are still insufficient. Further, the inclusion of such a great quantity of LED makes the light very bulky, and this is against the trend of being light-weighted and compact.
(4) Some conventional cargo lights use high brightness LED's to overcome the problem of insufficient lighting performance occurring in the conventional cargo light that uses LED's as light source. However, a different problem occurs. The high brightness LED generates a large amount of heat that must be dissipated by a heat dissipation device that is often bulky, making it not meeting the trend of being light-weighted and compact. In this respect, the present invention aims to provide a heat dissipation solution that enhances the heat dissipation performance and is not bulky.
(5) The conventional cargo light also suffers non-uniform irradiation of light, and this reduces the lighting performance thereof.
(6) The LED used in the conventional cargo lights is white LED. However, in case of refrigeration container truck, at the time the container door is opened, abrupt change of temperature between inside and outside of the container leads to interaction between heat and cold that leads to a white foggy atmosphere in which the white light emitting from the white LED is affected by the moist, often making it hard for an individual to obtain clear vision and thus affecting the movement of cargo.
(7) A truck is often equipped with various electricity consuming appliances and those appliances need to be switched ON/OFF timely. The switching operation of the appliances leads to variation of voltage supplied by the truck. For example, a refrigeration container cargo is equipped with a refrigerant pump that, when being switched ON/OFF, causes surge voltage or surge current, leading to significant variation of voltage and subjecting the cargo light of the truck to an impact caused by the voltage variation and eventually breaking the cargo light.
(8) For the purposes of making the cost reasonable, the conventional cargo light is made with a design that provides a structure that is strong enough to endure variation of temperature and resist vibration and impact (impact caused by instantaneous change of electricity).